A. Field of the Invention
The present invention relates to apparatus and methods for winding filament. In particular, the present invention relates to apparatus and methods for winding filament to create a filament-wound structure.
Within the specification, the term filament winding is used to describe the process in accordance with the invention. However, winding may actually be performed using “fiber bundles” comprising multiple individual filaments or fibers. Bundles may comprise a few filaments—as few as one—to as many as several million. Bundles of filaments are also called tows or rovings depending upon the material from which the filament is made. Therefore, the terms “fiber bundle” and “filament,” as used in this application, include both a single filament and bundles comprising multiple filaments.
B. Background of the Invention
In the aircraft industry, filaments are increasingly being used to form composite structures. For example, filaments are used to manufacture structures such as aircraft fuselages, aircraft empennages, and aircraft wings. In general, these filaments are lightweight and produce a smooth skin surface. This makes filaments ideal for the creation of structures with a smooth surface and low weight.
Typically, the manufacture of products using filaments includes the placement of filaments on a mandrel having a desired shape of a structure. The filaments are then cured or subjected to some other process to form the skin of the structure. In general, filament winding can be applied by a winding system or by hand. However, current apparatus and methods for manufacturing filament-wound structures have several disadvantages.
Current filament winding apparatus and methods tend to produce an uneven skin. This reduces the uniformity and smoothness of the structure. This reduced smoothness and uniformity also adversely affects the aerodynamics of the resulting structures because these problems create drag.
Current filament winding systems and methods also produce skins that are unduly thick. For example, most current winding machines cannot produce a structurally desirable skin thinner than 0.02 inches. This results in increased weight of the structure, which may hamper performance.
Some of these problems may be overcome by using hand placement. Hand placement of filaments may potentially be used to produce a thin, uniform skin. Hand placement of filaments, however, dramatically increases the costs of manufacturing these structures. Hand placed filaments are expensive to produce, and the labor costs associated with applying filaments by hand are very high.
The creation of filament winding apparatus and methods that could inexpensively produce a thin, uniform skin would therefore provide many advantages. For example, it would improve the smoothness of the structures, which would improve aerodynamics. It would also remove weight, which could improve performance. It would further be less costly to manufacture.
As for smoothness and uniformity, filament winding apparatus and methods that could produce a uniform skin on both simple and complex structures would improve the overall smoothness of the structure. If the skin is uneven, this reduces the overall smoothness of the structure. For aircraft structures, this can be a serious disadvantage. Therefore, apparatus and methods capable of winding a uniform skin on simple and complex structures would improve smoothness.
As for weight, a filament winding apparatus that could produce very thin skins would use less material. The use of less material results in lower weight. For example, most current systems cannot use a gauge tow lower than 5 mil (0.005 inches). Apparatus capable of winding gauge tows thinner than 5 mil would thus improve cost and weight.
As for cost, a thinner skin results in less weight, which results in less cost. Also, if hand placement can be avoided, costs would be further reduced.
Therefore, it is desirable to provide a winding apparatus capable of producing a thin, uniform, and inexpensive filament skin.
Apparatus and methods in accordance with the invention provide for a winding system capable of producing a thin, uniform, and inexpensive filament skin.